Various devices in downhole applications and in other fields use magnetic attraction or repulsion to accomplish various tasks. Some send a magnetic sonde downhole to trigger a valve to open simply from passing by, as is disclosed in U.S. Pat. No. 9,062,516. Other downhole applications mechanically move magnets between attracting and repelling orientations such as U.S. Pat. Nos. 9,322,233; 8,720,540 and US 2016/0208580. U.S. Pat. No. 8,191,634 uses repelling magnets as a shock absorber for a flapper type safety valve. US 2009/0151790 uses magnets to reposition a choke valve. Outside of downhole application magnetic force is used to close valves or passages as indicated in US 20100006788; U.S. Pat. Nos. 4,974,624 and 5,101,949.
Of more general interest are U.S. Pat. Nos. 6,394,180; 7,740,079; 8,955,605; 9,316,086; U.S. Patent Publication 2015/0101796; U.S. Patent Publication 2015/0267502 and U.S. Patent Publication 2016/0145957.
The present invention takes away the need to drop a ball and get it to land on a seat around a passage in a plug when performing a treatment that involves multiple plugs. In the past designs have been offered to loosely trap a ball above a seat using a spring to hold the ball off the seat until a predetermined flow creates a large enough reaction force to compress the spring and land the ball on the seat for a pressure treatment in the formation against the seated ball. While this design saves the time of delivery of the ball to the seat it presents other design issues which can be considerable drawbacks. For one there is the issue of the spring coils filling with debris which can prevent sufficient ball movement to reach the seat. The spring has its upper end laterally unsupported which can mean that the ball can spread the spring end apart rather than compressing the spring as desired with a result that the ball will again fail to reach the seat. Over long periods of use the spring can weaken and allow the ball to seat at an inopportune time. The advantages of using a magnet versus a spring/ball/cage system are: milling a spring can be difficult or can cause issues; more flow is achievable with openings in magnets than springs and the flow rate that triggers magnet movement is customizable and erosion can be a serious problem with springs which can be avoided with magnets.
The present invention keeps the path open to flow to a predetermined value with the force of repelling magnets keeping discs apart that have offset holes. One disc is guided for axial movement driven by fluid flow through its ports until a net force from flow is developed on the movable disc. Axial movement of one disc abuts the pair of discs and closes the ports due to their offset nature on the disc pair. The magnetic force is overcome to allow axial movement of one disc. On reduction of flow the magnetic force repels one disc to allow flow to resume. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.